XMM-Newton Observations of Luminous Sources in the Nearby ...

arXiv:1301.1040v1 [astro-ph.HE] 6 Jan 2013

XMM-Newton Observations of Luminous Sources in the Nearby Galaxies: NGC 4395, NGC 4736, and NGC 4258 A. Akyuz1 , S. Kayaci2 , H. Avdan1 , M. E. Ozel3 , E. Sonbas4 , S. Balman5 1

University of Cukurova, Department of Physics, 01330 Adana, Turkey 2 University of Erciyes, Department of Astronomy, Kayseri, Turkey 3 C ¸ a˘g University, Faculty of Arts and Sciences, 33800 Yenice, Tarsus, Mersin, Turkey 4 University of Adıyaman, Department of Physics, 02040 Adıyaman, Turkey 5 Middle East Technical University, Dept. of Physics, 06531 Ankara, Turkey [email protected]

ABSTRACT We present results from a study of the non-nuclear discrete sources in a sample of three nearby spiral galaxies (NGC 4395, NGC 4736, and NGC 4258) based on XMM-Newton archival data supplemented with Chandra data for spectral and timing analyses. A total of 75 X-ray sources has been detected within the D25 regions of the target galaxies. The large collecting area of XMM-Newton makes the statistics sufficient to obtain spectral fitting for 16 (about 20%) of these sources. Compiling the extensive archival exposures available, we were able to obtain the detailed spectral shapes of diverse classes of point sources. We have also studied temporal properties of these luminous sources. 11 of them are found to show short-term (less than 80 ks) variation while 8 of them show long-term variation within factors of ∼ 2 to 5 during a time interval of ∼ 2 to 12 years. Timing analysis provides strong evidence that most of these sources are accreting X-ray binary (XRB) systems. One source that has properties different than others was suspected to be a Supernova Remnant (SNR), and our follow-up optical observation confirmed it. Our results indicate that sources within the three nearby galaxies are showing a variety of source populations, including several Ultraluminous X-Ray Sources (ULXs), X-ray binaries (XRBs), transients together with a Super Soft Source (SSS) and a background Active Galactic Nucleus (AGN) candidate. Subject headings: binaries

1.

galaxies: individual(NGC4736, NGC4395, NGC4258)- X-rays: galaxies - X-rays:

ies such as M 31 (Pietsch 2005; Kong et al. 2002a, 2003b), M 33 (Pietsch 2004; Plucinsky et al. 2008) M 81 (Swartz et al. 2003), and M 101 (Pence et al. 2001; Jenkins et al. 2004). These sources are typically high and low mass X-ray binaries (XRBs), supernova remnants (SNRs), bright super soft sources (SSS), and a number of very luminous sources, so-called ultra-luminous X-ray sources (ULXs). For a study of discrete X-ray source population in the nearby spiral galaxies, a sample of three of them (NGC 4395, NGC 4736, and NGC 4258) were chosen for this work. All three have a low

Introduction

The increased imaging and energy resolution capabilities of the new generation X-ray observatories like XMM-Newton and Chandra, provide a better understanding of the X-ray emission from nearby galaxies. A combination of a number of discrete sources, hot interstellar gas, and a probable active galactic nucleus are thought to produce the observed X-ray emission from such galaxies (Fabbiano, 1989). Large number of discrete sources have already been detected by XMMNewton and Chandra in the disks of nearby galax-

1

activity Seyfert nucleus. Their low foreground absorption (1.20-1.43)×1020 cm−2 (Dickey & Lockman 1990) also made them good targets for exploring such discrete X-ray sources. NGC 4395 is classified as one of the nearest and least luminous (LBol ∼ 5×1040 erg s−1 ) Type 1 Seyfert galaxies (Filippenko & Sargent 1989). This dwarf galaxy appears to harbor a central black-hole, likely to be in the ∼ 104 -105 M⊙ range, significantly lower than more luminous Seyferts with black hole masses typically in the range ∼ 106 -108 M⊙ (Vaughan et al. 2005). Its nucleus has been the subject of several X-ray studies since the ROSAT observations (Moran et al. 1999; Lira et. al 1999). They have reported that its nuclear X-ray source displays a large amplitude variability on short time scales and has a soft X-ray spectrum. Also, five X-ray sources, one being significantly brighter than nucleus, were detected within ∼3′ of its nucleus. Later, observations by Chandra and XMM-Newton confirmed the variable nature of its active nucleus (Moran et al. 2005; Vaughan et al. 2005). Our next target, NGC 4736 (M94), is classified as a low luminosity galaxy with the closest sample of a low ionization nuclear emission-line (LINER) nucleus (Flippenko & Sargent 1985). Two bright sources were detected by ROSAT observations in its nuclear area (Cui et al. 1997). One of them was consistent with the nucleus of the galaxy and almost one-third of the total observed flux in (0.12) keV arose as the emission from the compact source in the center with an extended distribution of hot gas. 12 discrete sources (including galactic nucleus itself) were identified by ROSAT HRI data in its optical disk and ring regions (Roberts et al. 1999). The galaxy was also observed with the BeppoSAX in (0.1 - 100 keV) band and the Chandra ACIS-S for a high resolution study of its nuclear region (Pellegrini et al. 2002). They concluded that the LINER activity was due to a low luminosity AGN at the center. Eracleous et al. (2002) had already examined the high concentration of luminous sources in the nucleus of NGC 4736 by Chandra. They suggested that the galaxy was in a recent starburst phase where the emission was dominated by dense clusters of X-ray binaries. Our third target, NGC 4258 (M106) is a bright nearby Type 1.9 Seyfert galaxy. It is also known by its anomalous arms discovered by Hα imaging

(Courtes et al. 1993). Water maser line emission of rotating gas near its center indicated a mass of 3.6×107M⊙ in a disk of radius ranging from 0.12 to 0.25 pc (Miyoshi et al. 1995). ROSAT observations of NGC 4258 resolved the anomalous spiral arms forming the boundary of diffuse emission. 15 X-ray point sources associated with the galaxy were identified by ROSAT observations (Pietsch et al. 1994; Cecil et al. 1995; Vogler & Pietsch 1999). They could not detect the Seyfert nucleus of the galaxy as a point source. The first detection of active nucleus was reported by ASCA observations. It was modeled by an absorbed powerlaw spectrum of photon index Γ ∼1.8. The unabsorbed (2-10) keV luminosity of the source was LX = 4×1040 ergs−1 obscured by a column density of NH ∼ 1.5×1023 cm−2 . An Fe Kα emission line was detected with an equivalent width 0.25±0.10 keV (Makishima et al. 1994). NGC 4258 was also observed by XMM-Newton, which showed a hard nuclear point source that could be modeled by a highly absorbed power-law spectrum with no narrow Fe Kα emission (Pietsch & Read 2002). A series of observations were also made by Chandra to study its various properties (Young & Wilson 2004). They examined the spectrum of the low-luminosity active galactic nucleus, which was well described by a hard X-ray powerlaw and a variable luminosity with a constant thermal soft X-ray component. They also discussed the first detection of extragalactic Fe absorption line at 6.9 keV, with a very inclined accretion disk varying on a timescale of 6 ks. Yang et al. (2007) studied Chandra and XMM - Newton spectra of its anomalous arms and active jets. They confirmed that the X-ray emission from these arms has a thermal nature, suggesting that currently active jets could be responsible for heating the gas in the arms. In the present work, we will investigate the spectral and timing properties of the bright pointlike non-nuclear sources in these three galaxies, first as observed by XMM-Newton with a more extended database compared with the previous studies and later, by Chandra to supplement their spectral and timing properties. General properties of the galaxies are listed in Table 1. We will restrict ourselves to the off-nucleus luminous sources with sufficient signal to noise ratio (S/N) to perform spectral fitting. Source locations with re2

spect to the galaxy centers and their cross identifications (if any) have been listed in Table 2. The organization of paper will be as follows; In Section 2, we outline the data reduction and source selection criteria. In Section 3, the spectral fitting and timing analysis techniques are described and, in Section 4, detailed discussion of spectral and temporal results for individual sources in the galaxies are presented. The overall properties of their X-ray emission are discussed in Section 5. 2. 2.1.

son and identification. The detected point sources inside a D25 ellipse were specified as off-nuclear objects. We numbered them as XMM-n, n representing source number with decreasing pn count rate. Figures 1b, 2b, and 3b show XMM-Newton point source positions overlaid on a DSS1 optical blue image of each galaxy. Detected X-ray source parameters in each galaxy are summarized in Tables 4, 5, and 6 respectively. In each table the source ID (col.1), its position (col.2 & 3), the likelihood of existence (where a likelihood value of 10 corresponding to a detection probability above 4σ) (col.4), integrated (pn + MOS1 + MOS2) count rates with errors (col.5), flux with the error (col.6), and luminosity with the error (col.7) are given in the (0.2-12) keV band. The luminosities were calculated from the flux values using the distances indicated in Table 1.

Observations and Data reduction The XMM-Newton observation

The data used for the analysis were retrieved from the XMM-Newton public archive. XMMNewton Observatory (Jansen et al. 2001) has three EPIC cameras at its focal plane: one uses the pnCCD (Str¨ uder et al. 2001) and the other two MOS-CCD detectors (Turner et al. 2001). Instruments were operated in the full-frame imaging mode and used thin or medium filters for pn and MOS. We analyzed the pipeline-processed data by using the standard software tools of XMMNewton Science Analysis System (XMM-SAS) v 10.0 (Gabriel et al. 2004). In the SAS, X-ray events corresponding to PATTERN≤ 4 (singles and doubles) were then selected with FLAG==0 option for the pn camera, PATTERN≤ 12 were used for the MOS cameras. Source detection was performed using the standard maximum likelihood technique as implemented by SAS tool edetect− chain. Each source inside the D25 ellipse was checked to exclude false or doubtful sources, after the automatic selection procedure in SAS. The log of observations, including the dates, IDs, exposure times, and the type of EPIC camera for each target, are given in Table 3. In the analysis, we simultaneously used data from the EPIC pn and the EPIC MOS for each galaxy to determine the spectra of the sources (with the exception of the MOS data for NGC 4395, which has poor statistics). Note also that the EPIC pn has more source counts due to its better sensitivity when compared with the MOS detectors. Figures 1a, 2a, and 3a show the combined exposure-corrected EPIC pn, MOS1 and MOS2 true color images of the presently analyzed archival data for the sample galaxies. Inclination corrected D25 ellipses are also shown for compari-

2.2.

The Chandra observation

To study the spectral and temporal properties of the non-nuclear point sources, we complemented our XMM-Newton analysis with the Chandra data of each target galaxy. A separate observation log of the Chandra data is given in Table 7 for our galaxies. We retrieved the data from the public archive and analyzed with CIAO v4.3 software package using the CALDB v4.4.2 calibration database. All data were filtered to 0.3 - 10 keV energy range. The detection of the X-ray point sources was performed using the WAVDETECT task within the same package. We have run the task over the 1, 2, 4, 8 and 16-pixel wavelet scales, since these scales are appropriate for detecting point-like sources. After a visual examination for possible false detections, we have only taken into account the sources with detection significance of 3.5σ or better and with net counts higher than 6. It is well known that, Chandra has significantly better angular resolution than XMM-Newton. As a result, the detected XMM-Newton point sources (one or two) in the central region of galaxies may have overlapped several Chandra point sources. Since in the present analyses, we examined only the non-nuclear sources, the sources located in the central regions of 0.3′ radius were excluded in all three galaxies. We have started our Chandra data analysis with NGC 4395 and the detected 11 point sources in its D25 region. Only one source in the central re3

erlaw+blackbody (PL+BBODY), powerlaw+disk blackbody (PL+DISKBB), and powerlaw+mekal (PL+MEKAL). We also used a photoelectric absorption model as part of the fit. The fits were applied to data in the 0.2 - 10 keV range. The EPIC pn and MOS spectra were fitted simultaneously for each object only in galaxies NGC 4736 and NGC 4258. For NGC 4395 we used only the EPIC pn data due to low statistical quality of the MOS data. We used a constant parameter which was set free to account for the normalization differences in the flux calibration of the three EPIC cameras. To compare the spectral shapes of sources between XMM-Newton and Chandra observations, we fitted the same spectral models to all data. Each data set was chosen based on a longer exposure time to provide sufficient counts for spectral fitting. Standard CIAO routines were used to reprocess event lists; then source and background spectra were extracted to construct so called the RMF and ARF files. We have fitted the data of 13 Chandra sources in the three galaxies, however, only two of them (XMM-3 and XMM-6 in NGC 4258) were above the threshold (> 300 counts) for spectral analysis. Our results are consistent with the XMM-Newton analysis therefore, we have discussed only the spectral parameters of these two sources in NGC 4258 in Section 5.3.

gion of the galaxy has been excluded. From the remaining 10, several have coincided with corresponding XMM-Newton sources. Four of them were examined individually in Section 5.1 due to sufficient statistics provide by XMM-Newton observations. These four Chandra source positions are offset within 2′′ of XMM-Newton source positions center in the galaxy. When the same procedure was carried out for the other two galaxies we obtained the following: For NGC 4736, 43 point sources in the D25 region were detected. 15 sources which were in the central region have been excluded. From the remaining 28 several overlapped by XMM-Newton sources. Among are them, three sources coincided with XMM-Newton sources, which were examined individually in Section 5.2. XMM-Newton and Chandra source positions of these three agree within 2′′ in NGC 4736. For NGC 4258, 42 point sources were detected in the D25 region. Five point sources in the central region have been removed. Among the remaining, six sources have coincided with corresponding XMM-Newton sources, and they were examined individually in Section 5.3. XMM-Newton and Chandra source positions of these six did agree within ∼ 6 year period. It has a high unabsorbed luminosity of LX = 1.95×1039 erg s−1 revealing that this source can be a transient ULX.

XMM-6 and XMM-10: The spectra of these sources are best fitted with an absorbed PL model with a photon index of Γ = 1.42 and Γ = 1.86 respectively. Quite similar luminosity values of LX = 2.6 ×1038 erg s−1 and ∼ 1 ×1038 erg s−1 are also observed respectively. These two sources are at different distances from the central bulge of the galaxy, however we think that XMM-6 has a noticeable contribution from the galactic bulge material, which may explain the differences in spectral shapes and luminosities. We detected no definite variation in long-term light curve of XMM-6, but its short-term light curve satisfies our criteria of variability. XMM-10, does not show any definite indication of short-term variability although its long-term light curve does show some variability (a factor of ∼2). We can conclude that both 6

luminosity estimation for a one-component model is consistent with a ULX.

XMM-12: This source is located away from the disk of the galaxy and was detected earlier by ROSAT (Roberts et al. 1999). In our analysis its spectrum is adequately fitted by the onecomponent DISKBB model (Tin = 1.44 keV) with an unabsorbed luminosity of LX = 0.7×1038 erg s−1 . Although it does not show any short-term variability, in the long-term a variability within a factor of 3 can not be excluded. It could be an XRB source.

XMM-3: The location of this source is quite far from the disk (2.1′ ). This source was first detected by ROSAT (Pietsch et al 1994). It was also identified as a ULX by XMM-Newton (WMR2006) and Chandra (Swartz et al. 2004). According to WMR2006, the source is best fitted with a PL+ BB model (kT = 0.78 keV and Γ = 2.02) with a χ2ν value of 1.2 for the data in 2002. This source was identified by Chandra as (CXOU J121857.8+471607) with an absorbed PL model (Γ = 2). In our XMM-Newton analysis, the source spectrum is best fitted with a one component absorbed DISKBB (Tin = 1.28 keV) with a rather high unabsorbed luminosity of LX = 1.9 ×1039 erg s−1 . Our analysis of the Chandra data for this source also show that its spectrum is best fitted with a hot DISKBB model, (Tin = 1.31 keV) with a higher unabsorbed luminosity of LX = 2.8 ×1039 erg s−1 . Its short term light curve shows a significant variation, also its long-term light curve shows variation with a factor of ∼ 4. The high source luminosity, leads us to conclude that it is a ULX. We also note that the present analysis is based on a longer observation time with much better statistics than all earlier results.

XMM-18: This source was first observed by ROSAT (Roberts et al. 1999). It is located ∼2.1′ away from the central region of galaxy. The source spectrum is best fitted by a PL (Γ = 1.39) with an unabsorbed luminosity of LX = 0.7 ×1038 erg s−1 . While no significant variability is found in the short-term, in the long-term a variability pattern of up to a factor of 3 is noticeable. We suggest that this source is probably an XRB. 5.3.

NGC 4258

We detected 24 sources inside the D25 region of this galaxy (see Table 5). Our detection limiting flux is ∼ 5 ×10−15 erg cm−2 s−1 in the 0.2-12 keV energy band for sources inside the optical disk. More than half of these sources have high luminosity (LX > 1038 ergs−1 ). We derived one and two-component best-fitting spectral model parameters for the sources as given in Tables 14-15. The spectra the best fitting models for 8 of these sources are given in Figure 12. Individual source characteristics are given in the following:

XMM-6: This source is located 2.4′ away from the galactic center. Its spectrum is well fitted with an absorbed PL (Γ = 1.87) model. It has an unabsorbed luminosity of LX = 1.5×1039 erg s−1 . A single component model fitted to the Chandra data gives almost the same parameter (Γ = 1.87), and a similarly high luminosity ∼ 1×1039 erg s−1 helping to identify the source as an ULX (Shwartz et al. 2004). Our Chandra data analysis for this source also gives the same best fitted model (PL) and parameter with almost the same high luminosity value. Long term light curve of XMM-6 shows a factor of ∼ 3 variability between the intervals, and there is also strong evidence for short-term variability. This raises the possibility that it could be an accreting XRB in the galaxy. Interestingly, however, the same source also coincides with a blue stellar counterpart from DSS2 image making it a likely background AGN candidate. True nature of this

XMM-2: We find that this source is a transient ULX. Earlier XMM-Newton data was already interpreted by WMR2006 as a transient. The source has been detected for the first time in 2002 (ObsID 0059140901) and was not detected in other available observations. The sharp increase in count rates in 2002 data compared with previous (2000, 2001) and later (2006) upper limit leads us to firmly conclude its transient nature. The source also shows short-term variability. Its spectrum is best described by DISKBB (Tin = 1.43 keV) with a χ2ν value of 1.33 and a high unabsorbed luminosity, LX = 1.5 ×1039 erg s−1 . The spectral fit is not improved with an additional component. Our

7

source requires further study.

from main body of the galaxy and its spectrum is described by a PL with Γ ∼ 2 with an unabsorbed luminosity of LX = 3.3×1038 erg s−1 . Its short-term light curve shows significant level of variability, while its long-term data show a factor of ∼ 3 variation between observations. This source may also be a candidate XRB.

XMM-8: This source is best described by a two-component model. The spectral fit is improved over that of a simple PL (Γ = 2.1) fit by addition of a MEKAL component (Γ = 1.95 and kT = 0.57 keV). It has a high unabsorbed luminosity of LX = 1.2 ×1039 erg s−1 . To reveal its nature we also analyzed the Chandra archival data. Two different sources can be resolved within the same position by the better angular resolution of Chandra. However, due to the limited amount of data, it was not possible for us to carry out a satisfactory spectral analysis for these two separate sources. In the same neighborhood, two radio SNR candidates were identified by Hyman et al. (2001) (sources 10 and 12, Table 1) but none coinciding with our Chandra sources (angular separations ∼ 6′′ and ∼ 16′′ respectively). Both long-term and short-term light curves of data from the source region do show evidences of sometimes erratic variability. The spectral shape discussed above leads us to tentatively conclude that, the source region could harbor an XRB. However, further long duration observations with better angular resolution are surely needed to clarify the nature of the source(s).

XMM-21: In our analysis, this source was best fitted with a one-component absorbed PL model (Γ ∼ 2). Both its short-term and long-term data show strong evidence for variability. The source has an unabsorbed luminosity of LX = 2.0×1038 erg s−1 which suggest that this source is likely to be an XRB. However in the list of WMR2006 it was defined as a ULX. Its spectrum was fitted with a PL and a BREMSS equally well at a luminosity LX = 1.2×1039 erg s−1 . Therefore, further observations are needed to clarify its true nature. 6.

Discussion and Conclusions

In the above sections, we presented spectral and temporal analyses on the non-nuclear X-ray point sources in the three nearby galaxies, NGC 4395, NGC 4736, and NGC 4258 selected on the basis of their low hydrogen column densities with low activity Seyfert nuclei. Our main conclusions can be noted as follows: (1) Total number of point sources in the D25 area of each of these galaxies are similar (29 for NGC 4395, 21 for NGC 4736, and 23 for NGC4258). Data at hand however, allows spectral analysis for only a smaller number (a total of 16 out of 74) of these sources. Luminosity for these sources fall into the range (0.4 - 22.7)×1038 erg s−1 . 14 of these 16 sources have positions clearly indicating that they have no contamination from background or foreground objects or structures. (2) For comparison purposes, we have analyzed archival Chandra data of the three galaxies. 13 of these 16 XMM-Newton sources have also been detected by Chandra. Their source positions, in general, show a clear offset ∼ 2′′ from the center of XMM-Newton error circle (15′′ ). Only two of these 13 sources have been examined spectrally due to sufficient statistics provide by Chandra observations. (3) Four of these 16 sources are ULX candidates owing to their spectral characteristics and high lu-

XMM-10: This source is located far away (6.4′ ) from the central body of the galaxy. Its spectrum is best fitted with an absorbed PL model (Γ = 2.8, χ2ν = 0.9). The unabsorbed luminosity in this observation is LX = 9.2×1038 erg s−1 . Its short-term light curve shows no strong indication of variability. However, its long-term light curve do show a variability (an uninterrupted increase) by a factor of at least 5 over the time interval of a decade. This source could be an XRB. XMM-16: This source gives a best spectral fit with a PL model (Γ = 2.20). The unabsorbed X-ray luminosity is LX = 7.2×1038 erg s−1 . Shortterm light curve shows significant variability and the long-term data shows evidence of variability within a factor of ∼ 4 after 2002 in the next ∼ 4 years. The spectral parameters and variation of the source suggest that this may also be a candidate XRB. XMM-17: This source is located ∼ 2′ away 8

minosities. Two of these sources are in NGC 4258 (XMM-2 and XMM-3) and they are best fitted with an absorbed DISKBB model with a hot inner disk temperature (Tin ∼ 1.43 keV and 1.28 keV respectively). These values are within the range given for Galactic black-hole XRBs in the highstate emission (McClintock & Remillard 2006). On the other hand, 2 ULXs (XMM-2 in NGC 4736 and XMM-2 in NGC 4258) show significant transient behavior. The statistically significant improvement over a one-component fit is found in the PL+DISKBB model fit for the ULX in NGC 4736. The disk temperature is also cool (0.75 keV) in this case. Similar disk temperatures for ULX sources in M101 (Jenkins et al. 2004) and in the interacting pair galaxies NGC 4485/4490 (Gladstone & Roberts, 2009) were already found. Based on the argument that black hole masses scale inversely with accretion disc temperatures (Tin ∼ M−1/4 ), this was interpreted as evidence of intermediate mass black holes (IMBHs), with masses in the range of 102 -104 M⊙ for some ULX sources (Colbert & Mushotzky 1999). On the other hand, assuming spherical accretion onto a central blackhole in a binary system at the Eddington limit as suggested by Makishima et al (2000), our point source luminosities imply black hole masses in the stellar range of (2-15) M⊙ . This is consistent with Galactic stellar-mass black holes which were found to lie in the range of (2-23) M⊙ (McClintock & Remillard 2004). Most probably, these sources belong to the extreme end of the XRB population in their galaxies. Many similar luminous point sources in nearby galaxies are also reported (Jenkins et al. 2004; Gladstone & Roberts 2009). (4) Of the remaining 12 sources, 8 are best fitted with absorbed PL spectra (Γ = 1.4 - 2.8). They generally have luminosities around the Eddington limit (≥ 1038 ). Photon indices of 7 of these sources are in agreement with low/hard state black-hole XRBs (Tanaka 2001). Remaining 2 sources (XMM-10 and XMM-16 in NGC 4258) have steeper power-law slopes (Γ > 2) representing strong Comptonized thermal emission from a black-hole accretion disc (Jenkins et al. 2004, McClintock & Remillard 2004). Based on X-ray data these sources are considered to be black-hole XRBs. (5) The locations of the point sources could also provide clues to the nature of the X-ray emission;

however, at times they could also be misleading. Positions of our sources suggest that almost all are associated with their host galaxies except possibly one. As explained above, this latter source (XMM6 in NGC 4258) could be a background AGN due to its spectral shape (PL with Γ ∼ 1.9 which is typical of AGNs) and its coincidence with a stellar object (in corresponding DSS image), warranting further investigation. (6) A noticeable overall result of the spectral analysis of the sources from these three galaxies, is that X-ray sources from different classes can be distinguished. One source (XMM-5 of NGC 4395) is distinctly different from rest. A closer inspection by our optical follow up observation revealed that, it was indeed different type; an SNR with a best spectral fit to a VPSHOCK, typical of such objects (Sonbas et al. 2010). (7) We have identified only one SSS with typical low luminosity values around 5×1037 erg s−1 in one of these galaxies (XMM-23 in NGC 4395). This class of sources generally are known to be a white dwarf accreting at high rates resulting in nuclear burning on the surface with kT ∼ (10-100) eV (Di Stefano et al. 2004; Stiele et al. 2010). Our source also confirms these limits. (8) About half of presently analyzed sources show statistically significant short and long- term variabilities. This can be taken as evidence for the underlying binary nature of these sources. In more general terms, we can conclude that Xray astronomy as reached at a stage to differentiate several source types in the galaxies beyond our local group. With increasing statistics, the role of such sources in the evolution of stars and such galaxies will be clearer. Aysun Akyuz acknowledges support from the EU FP6 Transfer of Knowledge Project ”Astrophysics of Neutron Stars” (MKTD-CT-2006042722). We thank Frank Haberl and Nazim Aksaker for their very valuable help. We also thank the TUBITAK National Observatory (TUG) for their support for observing times and equipment. REFERENCES Borkowski, J. K. et al. 1996, ApJ, 466, 866 Cedres, B. and Cepa, J. 2002, A&A, 391, 809

9

Cecil, G. et al. 1995, ApJ, 452, 613

Miyoshi, M. et al. 1995, Nature, 377, 177M

Colbert, E. J. M and Mushotzky, R. F. 1999, ApJ, 519, 89

Moran, E. C. et al. 1999, PASP, 111, 801 Moran, E. C. et al. 2005, ApJ, 129, 2108

Courtes, G. et al. 1993, A&A, 268, 419

Pellegrini, P. S. et al. 2002, A&A, 383, 1

Cui, W. 1997, ApJ, 477, 693

Pence, W. D. et al. 2001, ApJ, 561, 189

Di Stefano, R. and Kong, A. K. H. 2003, ApJ, 592, 884

Pietsch, W. et al. 1994, A&A, 284, 386

Di Stefano, R. et al. 2004, APS,

Pietsch, W. and Read, A. M. 2002, A&A, 384, 793

Dickey, J. M. and Lockman, F. J. 1990, ARA&A, 28, 215

Pietsch, W. 2004, A&A, 426, 11

Eracleous, M. et al. 2002, ApJ, 565, 108

Plucinsky, P. P. et al. 2008, ApJS, 174, 366

Fabbiano, G. 1989, A&A, 27, 87

Roberts, T. P. et al. 1999, MNRAS, 304, 52

Filippenko, A. V. and Sargent, W. L. W. 1985, ApJS, 57, 503

Sonbas, E. et al. 2010, A&A, 517,

Pietsch, W. 2005, A&A, 434, 483

Stobbart, M. A.; Robert T. P. and Wilms, J. 2006, MNRAS, 368, 397

Filippenko, A. V. and Sargent, W. L. W. 1989, ApJ, 347, 11 Gabriel, C. et al. 2004, ASPC, vol. 314

Stiele, H. et al. 2010, Astron. Nachr./An 999, No 88, 789

Gladstone, T. C. and Roberts, T. P. 2009, MNRAS, 397, 124

Struder, R. et al. 2001, A&A, 375, L5 Swartz, D. A. et al. 2002, ApJ, 574, 382

Hyman, S. D. et al. 2001, ApJ, 551, 702

Swartz, D. A. et al. 2003, ApJS, 144, 213

Jansen, F. et al. 2001, A&A, 365, L1

Swartz, D. A. et al. 2004, ApJ, 154, 519

Jenkins, L. P. et al. 2004, MNRAS, 349, 404

Kong, A. K. H. et al. 2003, ApJ, 580, L25

Tanaka, Y. 2001, in Black Holes in Binaries and Galactic Nuclei, ed. L. Kaper, E. P. J. van den Heuvel, & P. A. Woudt (Berlin: Springer), 141

Leonidaki, I. et al. 2010, ApJ, 725, 842

Turner, L. J. M. et al. 2001, A&A, 365, L27

Lira, P. et al. 1999, MNRAS, 305, 109

Vaughan, S. et al. 2005, MNRAS, 356, 524

Liu, J. 2011, ApJS, 192, 10L

Vogler, A. and Pietsch, W. 1999, A&A, 352, 64

Makishima, K. et al. 1994, PASJ, 46, L77

Yang, Y. et al. 2007, ApJ, 660, 1106

Makishima, K. et al., 2000 ApJ, 535, 632

Young, A. J. and Wilson, A. S. 2004, ApJ, 601, 133

Kong, A. K. H. et al. 2002, ApJ, 557, 738

Mathewson, D. S. and Clarke, J. N. 1973, ApJ, 182, 697

Winter, L. M.; Mushotzky, R. F. and Reynolds, C. 2006, ApJ, 649, 730

McClintock, J. E. and Remillard, R. A. 2006, Compact Stellar X-ray Sources, eds. Lewin, W.H.G and van der Klis, Cambridge (CUP)

This 2-column preprint was prepared with the AAS LATEX macros v5.2.

10

(a)

(b)

Fig. 1.— In (a), XMM-Newton RGB image of NGC 4395. Colors stand for red (0.2-1) keV, green (1-2) keV and blue (2-12) keV. The D25 ellipse is also shown for comparison. In (b), XMM-Newton source positions are overlaid on a DSS1 optical blue image (circles are not representing positional error radii). The detected point sources inside the D25 ellipse are specified as off-nuclear galactic objects.

(b)

(a)

Fig. 2.— XMM-Newton RGB image of NGC 4736. Definitions are the same as in Figure 1.

(a)

(b)

Fig. 3.— XMM-Newton RGB image of NGC 4258. Definitions are the same as in Figure 1

11

Fig. 4.— XMM-Newton short-term light curves of NGC 4395 point sources. These light curves were obtained from the counts using only EPIC-pn camera. A dashed line shows the mean count rate and error bars correspond to 1σ deviations assuming Gaussian statistics.

Fig. 5.— XMM-Newton short-term light curves of NGC 4736 point sources. These light curves were obtained by summing the counts from the EPIC-pn and MOS cameras. A dashed line shows the mean count rate and error bars correspond to 1σ deviations assuming Gaussian statistics.

12

Fig. 6.— XMM-Newton short-term light curves of NGC 4258 point sources. These light curves were obtained by summing the counts from the EPIC-pn and MOS cameras. A dashed line shows the mean count rate and error bars correspond to 1σ deviations assuming Gaussian statistics.

13

(a)

(b)

(c)

Fig. 7.— XMM-Newton long-term light curves of NGC 4395, NGC 4736 and NGC 4258 as (a), (b) and (c) respectively. Data points were taken from XMM-Newton (circles), ROSAT PSPC (squares), ROSAT HRI (triangles), Chandra (stars) flux measurements have been converted to (0.5 - 2) keV flux as explained in the text. Flux upper limits are shown with downward arrows.

14

(a)

(b)

Fig. 8.— (a) short-term (b) long-term light curves of XMM-2 in NGC 4258. Properties and possible nature of this transient source are described in the text.

15

(a)

(b)

XMM−2 po+diskbb (Γ = 3.1, Tin= 0.19 keV)

XMM−5 VPSHOCK (kT= 3.98 keV)

Normalized Counts s−1 keV−1


0.01

0.01

10−3

10−3

10−4

10−5 10−4 2

2

0

χ

χ

0 −2

−2

−4

0.2 0.2

0.5

(c)

1 Channel Energy (keV)

0.5

2

(d)

XMM−6 power−law (Γ = 1.42)

1 2 Channel Energy (keV)

5

10




0.01

10−3

10−3

10−4

10−4

2 1

1 0 χ

0 χ

−1

−1

−2

−2 0.2

0.5


5

0.5

10


5

(e) XMM−23 blackbody (kT=0.06 keV)


0.01

10−3

10−4

10−5

10−61

χ

0 −1 −2 0.5


Fig. 9.— The best fitting model, spectra (upper panels), and the residuals between the data and the model in standard deviations (lower panels) of the sources in NGC 4395. Since the MOS data has poor statistics, only the EPIC-pn spectra have been obtained for these sources.

16

Fig. 10.— Optical spectrum of XMM5 in NGC 4395 obtained with the TFOSC instrument on RTT150 at TUG, Antalya, Turkey (a)

(b)


XMM−12 diskblackbody (Tin= 1.44 keV)

0.01 Normalized Counts s−1 keV−1


0.1

0.01

10−3

10−3

10−4

10−4

4 1 χ

χ

2 0

0

−2 −1 0.2

0.5


5

10

0.2

(c)

0.5


5

10


−3


10

10−4

10−5

10−6 2

χ

1 0 −1 0.2

0.5


5

10

Fig. 11.— The best fitting model, spectra (upper panels), and the residuals between the data and the model in standard deviations (lower panels) of the sources in NGC 4736. The EPIC-pn data points and best fitting model are shown in black; data from MOS1 and MOS2 are shown in green and red, respectively. 17

(a)

(b)


XMM−3 diskblackbody (Tin= 1.28 keV)



0.01 0.01

10−3

10−3

10−4

10−5

2

2

0 χ

χ

0

−2 −2 0.5


(c)

5

0.5

1

(d)



5

10

XMM−8 po+mekal (Γ = 1.95, kT= 0.57 keV)



0.01

10−3

10−4

10−5

0.01

10−3

10−6

2

1

1

0

χ

χ

10−4 10−7 2

0 −1

−1

−2

−2 0.5

1


(e)

5

10

0.2

0.5


(f)


5

10

XMM−16 power−law (Γ = 2.20) 0.1



0.01

10−3

−4

10

10−3

10−4

10−5 2

2

0

0

χ

χ

0.01

−2 −2 0.2

0.5


(g)

5

10

0.5


(h)


5

10




1

10−3 10−4 10−5 10−6

10−3 10−4 10−5 10−6

10−7

10−7

10−8

10−8 2

2

1 χ

χ

0

−2

0 −1

0.5

1


5

−2

10

0.5

1


5

10

Fig. 12.— The best fitting model, spectra (upper panels), and the residuals between the data and the model in standard deviations (lower panels) of the sources in NGC 4258. The EPIC-pn data points and the best fitting model are shown in black; data from MOS1 and MOS2 are shown in green and red, respectively. 18

Table 1 General properties of the sample galaxies studied in our work. RA, Dec. (J2000)

Hubble Type1

12:25:48.9 +33:32:47.8 12:50:52.6 +41:07:09.3 12:18:57.6 +47:18:13.4

SA(s)m (R)SA(r)ab SAB(s)bc

Galaxy NGC 4395 NGC 4736 NGC 4258

Distance2 (Mpc)

Inclination (deg.)

4.2 4.3 7.7

38 33 71

1

Winter et al. (2006)

2

Swartz et al. (2004), Winter et al. (2006)

3

Column density, obtained from the Web version of the nH FTOOL.

4

D25 diameter; defined by the 25 mag per square arcsec brightness level.

nH 20

3 −2

(10 cm 1.33 1.43 1.20

)

D25 corr 4 (arcmin) 13.3 11.8 14.2

Table 2 Locations of luminous sources (as defined in the text) with respect to the galaxy centers and cross identifications, for the sources in three galaxies studied. Galaxy

Source

Separation (arcmin.)

ROSAT ID

NGC 4395

XMM-2 XMM-5 XMM-6 XMM-10 XMM-23

2.9 2.1 0.7 2.0 1.9

P1a P2a P3a P4a

XMM-2 XMM-12 XMM-18

0.9 2.3 2.1

XMM-2 XMM-3 XMM-6 XMM-8 XMM-10 XMM-16 XMM-17 XMM-21

3.1 2.1 2.4 1.5 6.4 3.3 2.0 3.2

NGC 4736

NGC 4258

b

X-7 X-13b P16c

CHANDRA ID CXOU J122539.5+333204d CXOU J122549.063+333201.82e CXOU J122547.287+333447.75e CXOU J122545.271+333103.40e CXOU J125048.598+410742.49e CXOU J125047.618+410512.26e CXOU J125104.4+410725f CXOU J121857.8+471607d CXOU J121843.8+471731d

P14c P13c P15c

a

CXOU J121839.317+471919.27e CXOU J121849.481+471646.42e CXOU J121856.419+472125.56e

The 2RXP Catalog 2000. b Roberts et al. 1999. c Pietsch et al. 1993. d Swartz et al. 2004. e Liu 2011. f From present work.

19

Table 3 The log of XMM-Newton observations, for the three galaxies studied. Galaxy

ObsId

Obs. Date

Exposure1 (s)

Mode2 /Filter

NGC 4395

0112521901 0142830101

2002.05.31 2003.11.30

13978 89000

FF/Thin FF/Medium

NGC 4736

0094360701 0404980101

2002.06.26 2006.11.27

17046 37245

FF/Medium FF/Thin

NGC 4258

0110920101 0059140101 0059140201 0059140401 0059140901 0400560301

2000.12.08 2001.05.06 2001.06.17 2001.12.17 2002.05.22 2006.11.17

16548 9488 10058 11798 13646 62635

FF/Medium FF/Medium FF/Medium FF/Medium FF/Medium FF/Medium

∗

We used only the observations highlighted in bold for the spectral analysis. 1

A net good time for EPIC-pn after most prominent flares were cut.

2

FF: Full Frame.

20

Table 4 Parameters of the sources in NGC 4395 from XMM-Newton observation. Source

RA(J2000) (hh:mm:ss.ss)

Dec(J2000) (dd:mm:ss.s)

ML

Count Rate ct s−1

Flux erg cm−2 s−1

Luminosity erg s−1

XMM-17

12:25:20.49

+33:33:00.8

1.22E+03

1.53E-02±6.3E-04

3.47E-14±1.7E-15

6.24E+37±3.1E+36

XMM-55

12:25:22.18

+33:33:16.9

1.92E+02

5.81E-03±4.5E-04

1.49E-14±1.2E-15

2.68E+37±2.1E+36

XMM-184

12:25:29.06

+33:36:11.4

2.05E+01

1.83E-03±3.2E-04

4.39E-15±9.4E-16

7.90E+36±1.7E+36

XMM-107

12:25:29.26

+33:29:01.3

8.88E+01

3.65E-03±3.8E-04

7.82E-15±1.0E-15

1.40E+37±1.8E+36

XMM-43

12:25:34.45

+33:32:11.8

2.32E+02

4.65E-03±3.5E-04

1.32E-14±1.0E-15

2.37E+37±1.8E+36

XMM-113

12:25:35.28

+33:28:31.5

7.00E+01

3.0E-03±4.2E-04

7.35E-15±1.0E-15

1.32E+37±1.8E+36

XMM-147

12:25:39.25

+33:33:49.8

4.58E+01

1.42E-03±2.0E-04

3.84E-15±6.2E-16

6.91E+36±1.1E+36

XMM-5

12:25:39.55

+33:32:04.1

5.35E+03

3.63E-02±7.5E-04

8.23E-14±2.0E-15

1.48E+38±3.6E+36

XMM-99

12:25:41.09

+33:31:09.4

3.62E+01

1.97E-03±2.7E-04

4.82E-15±7.3E-16

8.67E+36±1.3E+36

XMM-109

12:25:43.63

+33:35:07.0

6.69E+01

1.52E-03±2.0E-04

3.30E-15±5.5E-16

5.94E+36±9.9E+35

XMM-145

12:25:43.79

+33:28:54.4

6.23E+01

2.59E-03±3.0E-04

5.75E-15±8.2E-16

1.03E+37±1.4E+36

XMM-16

12:25:43.95

+33:30:00.2

1.08E+03

1.32E-02±5.2E-04

3.30E-14±1.5E-15

5.94E+37±2.7E+36

XMM-23

12:25:45.11

+33:31:04.6

6.43E+02

7.82E-03±4.0E-04

1.95E-14±1.1E-15

3.51E+37±1.9E+36

XMM-41

12:25:47.05

+33:36:07.4

2.85E+02

5.50E-03±3.6E-04

1.38E-14±1.0E-15

2.48E+37±1.8E+36

XMM-10

12:25:47.20

+33:34:47.4

1.51E+03

1.68E-02±5.5E-04

4.00E-14±1.5E-15

7.20E+37±2.7E+36

XMM-199

12:25:48.70

+33:28:39.3

1.32E+01

1.08E-03±2.1E-04

1.74E-15±5.1E-16

3.13E+36±9.1E+35 2.37E+38±5.9E+36

XMM-6

12:25:49.00

+33:32:03.5

2.30E+03

4.02E-02±1.1E-03

1.32E-13±3.3E-15

XMM-60

12:25:54.08

+33:29:05.9

1.82E+02

4.52E-03±3.4E-04

1.03E-14±9.7E-16

1.85E+37±1.7E+36

XMM-32

12:25:54.44

+33:30:47.0

6.10E+02

1.29E-02±5.8E-04

3.20E-14±1.6E-15

5.76E+37±2.8E+36

XMM-114

12:25:57.32

+33:29:47.1

5.50E+01

2.50E-03±3.1E-04

6.17E-15±9.2E-16

1.11E+37±1.6E+36

XMM-66

12:25:57.35

+33:30:39.8

8.77E+01

2.31E-03±2.5E-04

4.42E-15±7.2E-16

7.95E+36±1.3E+36

XMM-155

12:25:57.98

+33:36:09.8

1.34E+01

1.05E-03±2.2E-04

2.88E-15±6.2E-16

5.18E+36±1.1E+36

XMM-100

12:25:58.87

+33:28:23.7

9.08E+01

3.68E-03±3.6E-04

8.71E-15±1.0E-15

1.56E+37±1.8E+36

XMM-24

12:25:59.79

+33:33:22.0

5.43E+01

5.82E-03±5.6E-04

1.35E-14±1.5E-15

2.43E+37±2.7E+36

XMM-2

12:26:01.42

+33:31:32.0

1.34E+05

4.15E-01±2.3E-03

9.12E-13±6.2E-15

1.64E+39±1.1E+37

XMM-86

12:26:04.10

+33:32:50.6

6.42E+01

1.85E-03±3.4E-04

7.96E-15±9.7E-16

1.43E+37±1.7E+36

XMM-201

12:26:13.79

+33:33:45.9

1.36E+01

1.47E-03±2.6E-04

3.79E-15±7.4E-16

6.82E+36±1.3E+36

XMM-215

12:26:15.83

+33:33:48.0

1.44E+01

1.28E-03±2.4E-04

2.80E-15±6.5E-16

5.04E+36±1.1E+36

XMM-135

12:26:16.42

+33:30:18.2

3.74E+01

1.81E-03±2.6E-04

4.05E-15±7.3E-16

7.29E+36±1.3E+36

Note.—The sources are ordered by increasing right ascension (RA). Column 1: Source ID; Column 2-3: source coordinates; Column 4: likelihood of existence; Column 5: integrated EPIC pn and MOS count rates and errors in the 0.2-12 keV band; Column 6-7: Flux and Luminosity in the 0.2-12 keV band.

21




ML

Count Rate ct s−1



XMM-58

12:50:27.02

+41:05:07.5

7.49E+01

6.47E-03±9.1E-04

3.30E-15±1.2E-15

6.89E+36±2.5E+36

XMM-31

12:50:33.10

+41:05:12.8

1.48E+02

9.58E-03±8.5E-04

2.30E-14±2.4E-15

4.80E+37±5.0E+36

XMM-73

12:50:34.93

+41:07:43.7

3.16E+01

3.94E-03±5.7E-04

7.76E-15±1.4E-15

1.62E+37±2.9E+36

XMM-19

12:50:35.25

+41:10:26.4

2.42E+02

1.086E-02±8.3E-04

2.92E-14±2.4E-15

6.10E+37±5.0E+36

XMM-63

12:50:35.73

+41:06:43.9

3.54E+01

3.81E-03±5.8E-04

1.08E-14±1.7E-15

2.25E+37±3.5E+36

XMM-76

12:50:37.69

+41:10:37.9

3.48E+01

3.80E-03±5.7E-04

9.42E-15±1.6E-15

1.96E+37±3.3E+36

XMM-12

12:50:47.72

+41:05:10.8

5.28E+02

1.95E-02±1.0E-03

4.45E-15±2.8E-15

9.30E+36±5.8E+36

XMM-41

12:50:48.00

+41:08:35.1

2.25E+01

4.29E-03±6.6E-04

9.24E-15±1.7E-15

1.93E+37±3.5E+36

XMM-2

12:50:48.64

+41:07:40.5

4.77E+04

5.62E-01±4.4E-03

1.31E-12±1.2E-14

2.73E+39±2.5E+37

XMM-72

12:50:50.14

+41:11:29.4

2.39E+01

3.00E-03±5.3E-04

8.41E-15±1.5E-15

1.75E+37±3.1E+36

XMM-3

12:50:50.27

+41:07:10.1

2.63E+03

1.39E-01±2.8E-03

3.31E-13±7.9E-15

6.91E+39±1.6E+37

XMM-36

12:50:52.57

+41:02:52.7

1.92E+02

9.27E-03±8.5E-04

2.18E-14±2.3E-15

4.55E+37±4.8E+36

XMM-24

12:50:53.00

+41:08:43.5

1.06E+01

3.41E-03±6.8E-04

8.63E-15±1.8E-15

1.80E+37±3.7E+36

XMM-56

12:50:53.48

+41:04:55.2

4.19E+01

4.40E-03±5.8E-04

9.79E-15±1.5E-15

2.04E+37±3.1E+36

XMM-6

12:50:53.67

+41:06:34.2

3.57E+02

7.34E-02±3.5E-03

1.67E-13±9.6E-15

3.49E+38±2.0E+37

XMM-39

12:50:54.24

+41:09:06.4

4.94E+01

3.35E-03±4.6E-04

5.70E-15±1.1E-15

1.19E+37±2.2E+36

XMM-4

12:50:56.10

+41:06:55.9

3.55E+03

4.16E-01±7.4E-03

9.44E-13±2.0E-14

1.97E+39±4.1E+37

XMM-11

12:50:59.87

+41:02:53.8

5.45E+02

8.49E-03±6.4E-04

3.70E-15±9.6E-15

7.73E+36±2.0E+37

XMM-44

12:51:02.00

+41:03:04.7

9.74E+01

5.98E-03±6.2E-04

1.51E-14±1.8E-15

3.15E+37±3.7E+36

XMM-18

12:51:04.43

+41:07:26.0

2.10E+02

9.90E-03±7.6E-04

2.67E-14±2.2E-15

5.58E+37±4.5E+36

XMM-27

12:51:09.01

+41:02:57.8

2.37E+02

9.96E-03±7.7E-04

2.63E-14±2.2E-15

5.49E+37±4.5E+36

Note.—Definitions are the same as in Table 4.

22




ML

Count Rate ct s−1



XMM-16

12:18:39.38

+47:19:19.1

2.37E+03

5.02E-02±1.4E-03

1.23E-13±3.9E-15

7.19E+38±2.2E+37

XMM-93

12:18:42.24

+47:23:46.9

4.19E+01

3.15E-03±5.2E-04

7.33E-15±1.5E-15

4.28E+37±8.7E+36 1.26E+39±2.6E+37

XMM-6

12:18:43.94

+47:17:31.7

6.91E+03

8.78E-02±1.6E-03

2.16E-13±4.5E-15

XMM-25

12:18:45.44

+47:18:32.1

1.28E+03

1.22E-01±3.4E-03

3.06E-13±9.7E-15

1.79E+39±5.6E+37

XMM-10

12:18:45.48

+47:24:20.5

5.06E+03

7.96E-02±1.8E-03

2.15E-13±5.6E-15

1.25E+39±3.2E+37

XMM-33

12:18:45.78

+47:18:07.5

3.44E+01

6.05E-03±7.7E-04

1.40E-14±2.0E-15

8.19E+37±1.1E+37

XMM-27

12:18:46.00

+47:23:12.9

7.49E+02

1.94E-02±9.2E-04

4.45E-14±2.5E-15

2.60E+38±1.4E+37

XMM-26

12:18:47.29

+47:20:22.0

4.09E+02

1.47E-02±8.2E-04

3.59E-14±2.2E-15

2.10E+38±1.2E+37

XMM-2

12:18:47.57

+47:20:53.8

3.26E+04

1.64E-01±4.1E-03

4.44E-13±1.2E-14

2.59E+39±7.0E+37

XMM-67

12:18:48.46

+47:22:26.1

8.41E+01

5.10E-03±5.4E-04

1.02E-14±1.4E-15

5.96E+37±8.1E+36

XMM-17

12:18:49.55

+47:16:46.6

1.41E+03

3.29E-02±1.0E-03

8.13E-14±3.0E-15

4.75E+38±1.7E+37

XMM-38

12:18:53.68

+47:17:24.5

8.64E+01

7.18E-03±7.4E-04

1.98E-14±2.1E-15

1.15E+38±1.2E+37

XMM-8

12:18:54.72

+47:16:49.4

4.93E+03

9.35E-02±1.8E-03

2.43E-13±5.6E-15

1.42E+39±3.2E+37

XMM-104

12:18:54.79

+47:13:59.7

2.24E+01

2.23E-03±4.6E-04

6.46E-15±1.4E-15

3.77E+37±8.1E+36

XMM-51

12:18:55.14

+47:23:02.5

1.90E+02

8.50E-03±6.6E-04

2.13E-14±1.8E-15

1.24E+38±1.0E+37

XMM-82

12:18:56.27

+47:15:08.1

5.03E+01

4.15E-03±5.1E-04

8.74E-15±1.3E-15

5.11E+37±7.6E+36

XMM-21

12:18:56.34

+47:21:25.6

1.46E+03

3.00E-02±1.0E-03

7.15E-14±2.8E-15

4.18E+38±1.6E+37

XMM-41

12:18:57.93

+47:16:56.7

1.70E+01

2.68E-03±4.4E-04

5.94E-15±1.1E-15

3.47E+37±6.4E+36

XMM-3

12:18:57.94

+47:16:07.7

1.36E+04

1.33E-01±1.9E-03

3.37E-13±5.5E-15

1.97E+39±3.2E+37

XMM-20

12:18:57.96

+47:19:07.4

9.25E+01

1.40E-02±1.2E-03

3.13E-14±3.2E-15

1.83E+38±1.8E+37

XMM-91

12:19:04.35

+47:14:53.3

5.58E+01

3.36E-03±5.1E-04

8.06E-15±1.4E-15

4.71E+37±8.1E+36

XMM-54

12:19:04.90

+47:16:03.9

1.53E+02

5.02E-03±4.8E-04

9.43E-15±1.3E-15

5.51E+37±7.6E+36

XMM-102

12:19:13.23

+47:14:11.2

2.59E+01

2.87E-03±4.2E-04

7.90E-15±1.3E-15

4.62E+37±7.6E+36

XMM-87

12:19:18.59

+47:16:14.7

3.12E+01

2.66E-03±4.0E-04

5.57E-15±1.0E-15

3.25E+37±5.8E+36

Note.—Definitions are the same as in Table 4.

Table 7 The log of Chandra observations, for the three galaxies studied. Galaxy

ObsId

Obs. Date

Exposure (ks)

Instrument

NGC 4395

882

2000.06.20

20.0

ACIS-S

NGC 4736

808 9553

2000.05.13 2008.02.16

50.0 25.7

ACIS-S ACIS-I

NGC 4258

350 1618 2340

2000.04.17 2001.05.28 2001.05.29

14.5 22.0 7.0

ACIS-S ACIS-S ACIS-S

23

Table 8 XMM-Newton short-term source variability χ2 test results, for the three galaxies studied. Galaxy NGC 4395

NGC 4736

NGC 4258

Source XMM-2 XMM-5 XMM-6 XMM-10 XMM-23 XMM-2 XMM-12 XMM-18 XMM-2 XMM-3 XMM-6 XMM-8 XMM-10 XMM-16 XMM-17 XMM-21

Bin size (s) 400 900 1200 2000 4500 200 2200 3000 900 700 750 1100 1500 1500 2500 2000

24

χ2 statistic χ /dof Pχ2 (var) 2

254/222 114/98 100/74 29/44 23/19 880/194 17/17 9/12 55/27 155/91 223/85 94/58 47/42 68/42 41/25 142/32

97.6 per cent >99.9 per cent >99.9 per cent >99.9 per cent >99.9 per cent 99.8 per cent 99.3 per cent 97.7 per cent >99.9 per cent

Table 9 Spectral parameters obtained with one-component model fits for point sources in NGC 4395. Source

model

NH (10 )cm−2

Γ

22

XMM-2

XMM-5

XMM-6

XMM-10

XMM-23

BBODY PL DISKBB BREMSS

0.03+0.01 −0.01 0.26+0.03 −0.03 0.07+0.01 −0.01 0.12+0.02 −0.01

BBODY PL DISKBB BREMSS VPSHOCK

0.04 0.31 0.18 0.12 +0.02 0.06−0.01


0.00 +0.02 0.06−0.02 0.03 0.04+0.02 −0.01


0.00 +0.04 0.15−0.05 0.02 0.01+0.04 −0.03


+0.22 0.28−0.01 +0.14 0.17−0.14 0.17+0.08 −0.06 0.21+0.07 −0.05

4.27+0.26 −0.23

kT keV

χ2 /dof

0.20+0.006 −0.007 0.26+0.01 −0.01 +0.04 0.47−0.04 0.26

3.62 0.67 0.35 +2.20 3.98−0.91 0.59 +0.09 1.42−0.09

+0.20 1.89−0.35 +18.00 18.9−7.50

0.47 +0.15 1.86−0.17

+0.30 1.22−0.24 5.39+4.03 −1.80 +0.03 0.06−0.02

6.87+2.30 −1.83

0.09+0.02 −0.02 +0.10 0.12−0.08

F (10−13 ) erg cm−2 s−1

L (1038 ) erg s−1

253.60/142 209.13/142 224.29/142 206.86/142

3.43 6.36 5.23 8.37

6.20 11.51 9.46 15.14

137.22/58 128.66/58 129.77/58 127.49/58 106.32/71

0.39 4.27 0.93 0.58 0.52

0.70 7.72 0.68 1.05 1.08

188.68/56 63.32/56 74.58/56 62.18/56

0.71 1.45 1.20 1.37

1.28 2.62 2.17 2.47

59.16/29 27.12/29 33.81/29 31.21/29

0.19 0.51 0.31 0.40

0.34 0.92 0.56 0.72

12.94/10 12.49/10 11.57/10 11.67/10

0.33 0.98 0.62 0.61

0.60 0.17 0.27 0.23

Note.—The best-fitting model for each source is highlighted in bold.

25

Table 10 Spectral parameters obtained using two-component model fits for point sources in NGC 4395 Source

model

NH (10 )cm−2

Γ

kT keV

χ2 /dof

22

F (10−13 ) erg cm−2 s−1

L (1038 ) erg s−1

XMM-2

PL+BBODY PL+DISKBB PL+MEKAL

0.29+0.04 −0.04 +0.04 0.15−0.03 +0.03 0.18−0.02

4.41+0.32 −0.29 +0.43 3.11−0.36 +0.19 3.80−0.15

0.09+2.74 −0.004 +0.02 0.19−0.02 +0.07 0.64−0.07

206.75/140 171.80/140 168.06/140

12.8 12.3 23.1

23.16 22.26 41.81

XMM-5


0.12+0.03 −0.05 0.28 0.42+0.05 −0.08

1.71+0.65 −0.56 3.44 3.40+0.41 −0.20

0.20+0.02 −0.03 0.06 0.17+0.02 −0.02

98.02/56 128.78/56 88.59/56

0.72 0.08 5.96

1.30 0.14 10.78

XMM-6


0.05+0.08 −0.04 0.04+0.04 −0.03 0.14+0.11 −0.04

1.40+0.10 −0.09 1.34+1.91 −0.42 4.43+1.25 −1.56

199.36 1.25+1.25 −1.25 14.16+20.25 −5.75

61.73/54 60.30/54 56.21/54

1.45 1.37 2.36

2.67 2.47 4.27

XMM-10


0.16+0.09 −0.06 0.14+0.06 −0.03 0.13+0.05 −0.06

1.95+0.33 −0.50 1.83+0.30 −0.20 1.66+0.32 −0.20

28.88+28.90 −28.90 0.005 0.60+0.22 −0.41

26.80/27 26.78/27 22.11/27

0.56 0.03 4.94

1.01 0.04 8.94

XMM-23


0.30+0.26 −0.11 1.05 0.26+0.26 −0.17

7.17+7.17 −2.05 0.90 6.55+6.55 −7.46

2.19+2.19 −2.19 0.12 0.08+0.18 −0.08

9.94/8 19.80/8 10.06/8

18.68 0.10 6.66

33.81 0.18 12.04

Note.—The best-fitting model for each source is highlighted in bold.

Table 11 Relative line intensities and spectroscopic parameters obtained from TUG observations for the SNR candidate source XMM-5 in NGC 4395 Line

XMM5

Hα(λ6563) SII(λ6716) SII(λ6731) OI(λ6300) OII(λλ7320,7330) E(B−V ) I(Hα ) (SII(λ6716)+SII(λ6731))/Hα

100 30.8 11.3 221.7 413 0.02 2.3E-13 0.42

26

erg cm−2 s−1


model

NH (10 )cm−2

Γ

XMM-2

PL DISKBB BREMSS

0.09+0.009 −0.007 < 0.008 0.03+0.004 −0.003

2.15+0.04 −0.03

XMM-12

PL DISKBB BREMSS

0.04+0.04 −0.04 +0.06 0.01−0.01 +0.04 0.03−0.03

1.47+0.31 −0.23

XMM-18

PL DISKBB BREMSS

+0.06 0.09−0.09 +0.05 0.02−0.02 0.07+0.05 −0.07

+0.26 1.39−0.19

χ2 /dof

F (10−13 ) erg cm−2 s−1

L (1038 ) erg s−1

768.60/519 695.47/519 534.87/519

1.20 6.72 8.53

2.77 15.52 19.70

+0.38 1.44−0.19 12.95+11.43 −7.43

16.17/19 17.09/19 15.69/19

0.54 0.23 0.42

1.24 0.73 0.97

1.97+0.55 −0.98 +25.61 25.54−18.02

17.42/20 19.80/20 17.58/20

0.31 0.24 0.29

0.71 0.50 0.66

kT keV

22

+0.02 0.87−0.02 +0.17 3.07−0.16

Note.—Sources in this galaxy can not be modelled by a BBODY model. The best-fitting model is highlighted in bold.

Table 13 Spectral parameters obtained with two-component model fits for point sources in NGC 4736. Source

model

NH (10 )cm−2

Γ

kT keV

χ2 /dof

22

F (10−13 ) erg cm−2 s−1

L (1038 ) erg s−1

XMM-2


0.03+0.005 −0.006 +0.008 0.02−0.006 0.06+0.008 −0.009

1.92+0.07 −0.06 +0.14 1.72−0.13 +0.06 2.05−0.06

0.44+0.03 −0.03 +0.06 0.75−0.04 +0.44 2.55−0.35

576.06/517 530.81/517 718.94/517

8.97 8.44 9.92

20.72 19.49 24.51

XMM-12


0.05+0.08 −0.05 0.09+0.12 −0.08 0.05+0.29 −0.05

1.81+2.22 −0.86 1.57+0.42 −0.32 5.64+0.48 −0.22

0.98+0.98 −0.98 0.04+1.07 −0.04 10.70

15.48/17 15.52/17 15.77/17

0.54 0.67 1.14

1.23 1.40 2.63

XMM-18


0.44+0.68 −0.39 0.54+0.64 −0.44 0.31+0.60 −0.12

1.58+0.88 −0.49 1.66+0.81 −0.54 1.45+0.50 −0.34

0.09+0.14 −0.03 0.10+0.16 −0.01 0.24 0.21−0.06

14.62/18 14.78/18 13.60/18

1.24 3.29 5.30

2.59 6.87 11.07

Note.—The best-fitting model is highlighted in bold.

27


model

NH (10 )cm−2

Γ

PL DISKBB BREMSS

0.18+0.07 −0.06 +0.03 0.02−0.02 +0.04 0.11−0.04

1.90+0.21 −0.22

PL DISKBB BREMSS

0.56+0.07 −0.06 +0.05 0.27−0.03 +0.05 0.41−0.04

2.19+0.07 −0.07

PL DISKBB BREMSS

+0.03 0.21−0.03 +0.01 0.06−0.01 0.15+0.02 −0.02

+0.09 1.87−0.09

PL DISKBB BREMSS

0.12+0.02 −0.02 0.01 0.05+0.01 −0.01

2.19+0.14 −0.12

PL DISKBB BREMSS

+0.05 0.58−0.05 +0.10 0.27−0.10 0.39+0.04 −0.03

+0.15 2.80−0.14

PL DISKBB BREMSS

+0.04 0.27−0.04 +0.02 0.07−0.02 0.14+0.03 −0.02

+0.18 2.20−0.15

PL DISKBB BREMSS

+0.03 0.15−0.03 0.05 0.09+0.02 −0.01

+0.12 1.99−0.10

PL DISKBB BREMSS

+0.03 0.08−0.03 0.00 0.02+0.02 −0.01

+0.11 1.99−0.09

kT keV

22

XMM-2∗

XMM-3

XMM-6

XMM-8

XMM-10

XMM-16

XMM-17

XMM-21

a

χ2 /dof

F (10−13 ) erg cm−2 s−1

L (1038 ) erg s−1

+0.30 1.43−0.25 +2.86 5.50−1.74

31.80/22 29.28/22 29.91/22

3.96 2.53 3.14

23.87 15.25 18.96

+0.05 1.28−0.05 +0.30 3.91−0.39

297/231 221.14/231 237.76/231

6.60 3.23 4.23

39.77 19.46 25.49

1.39+0.10 −0.09 5.60+1.17 −0.84

136.61/142 161.22/142 135.84/142

2.57 1.63 2.03

15.48 9.82 12.23

0.83 3.20+0.56 −0.47

125.29/109 249.70/109 166.01/109

2.04 1.01 1.37

12.28 6.08 8.25

0.84+0.10 −0.09 2.00+0.26 −0.23

87.67/96 87.16/96 86.82/96

1.54 1.83 2.61

9.28 11.02 15.73

0.85+0.10 −0.10 2.59+0.53 −0.45

99.78/76 146.78/76 117.96/76

1.20 0.68 0.94

7.23 4.10 5.72

1.10 4.32+1.09 −0.88

117.13/80 169.73/80 131.37/80

0.95 0.55 0.72

3.31 3.31 4.34

85.67/78 100.56/78 81.61/78

0.34 0.20 0.29

2.05 1.20 1.74

0.93+0.10 −0.10 4.07+1.15 −0.89 .

The spectra of this source was obtained by using only the EPIC-pn data

Note.—Sources in this galaxy can not be modelled by a BBODY model and the best-fitting model for each source is highlighted in bold.

28

Table 15 Spectral parameters obtained with two-component model fits for point sources in NGC 4258 Source

model

NH (10 )cm−2

Γ

kT keV

22

χ2 /dof

F (10−13 ) erg cm−2 s−1

L (1038 ) erg s−1

XMM-2∗


0.16+0.14 −0.15 0.11+0.34 −0.05 0.10+0.05 −0.04

2.24+0.27 −0.72 2.12+1.59 −1.59 9.45+9.89 −9.89

0.88+0.55 −0.40 1.40+1.12 −0.47 4.25+1.44 −0.89

27.76/20 27.35/20 37.11/20

4.05 2.80 7.89

24.42 16.88 47.57

XMM-3


0.37+0.10 −0.09 0.28+0.02 −0.02 0.75+0.17 −0.08

2.16+0.10 −0.22 0.67+19.67 −9.67 2.37+0.13 −0.07

0.76+0.08 −0.07 1.23+0.06 −0.06 0.14+0.08 −0.02

244.56/229 219.18/229 278.16/229

4.39 3.28 4.82

19.76 19.76 29.05

XMM-6


0.21+0.05 −0.03 0.23+0.26 −0.08 0.19+0.19 −0.02

1.97+0.24 −0.16 2.27+2.26 −0.68 1.80+0.21 −0.12

0.94+0.64 −0.37 2.04+2.66 −1.38 4.12

133.26/140 133.54/140 135.64/140

2.30 2.42 2.22

13.85 14.58 13.37

XMM-8


0.28+0.09 −0.04 0.12+0.02 −0.02 +0.02 0.09−0.01

3.57+0.30 −0.46 2.19+0.14 −0.12 +0.07 1.95−0.13

1.44+0.35 −0.26 0.00 +0.05 0.57−0.04

94.53/107 124.87/107 105.93/107

7.84 2.86 1.96

47.24 17.23 11.81

XMM-10


0.58+0.06 −0.05 0.56+0.23 −0.24 0.58+0.08 −0.08

2.79+0.17 −0.14 3.05+2.00 −1.02 2.94+0.25 −0.29

199.36 0.99+0.46 −0.41 2.95+0.42 −0.51

81.24/92 77.65/92 79.81/92

5.19 5.13 1.85

31.27 30.91 11.14

XMM-16


0.29+0.05 −0.05 0.27+0.32 −0.08 0.17+0.04 −0.04

2.61+0.24 −0.35 2.47+0.08 −0.08 2.09+0.10 −0.14

199.36 0.98+0.03 −0.05 0.65+0.19 −0.22

99.31/74 101.47/74 76.69/74

2.16 1.6 0.43

13.02 9.64 2.59

XMM-17

PL+BB PL+DISKBB PL+MEKAL

0.20+0.17 −0.05 0.30+0.14 −0.08 0.07+0.04 −0.03

1.69+0.33 −0.18 1.74+0.19 −0.24 1.68+0.17 −0.14

0.14+0.03 −0.04 0.16+0.05 −0.04 3.32+0.12 −0.09

101.54/78 101.55/78 76.36/78

1.12 1.83 0.42

6.75 11.03 2.53

XMM-21

PL+BB PL+DISKBB PL+MEKAL

0.10+0.05 −0.08 0.13+0.05 −0.04 0.06+0.05 −0.04

2.21+1.03 −0.16 2.12+0.21 −0.19 1.91+0.24 −0.26

0.97+0.12 −0.09 0.02+0.01 −0.01 2.90+2.91 −2.91

84.56/76 80.06/76 94.63/76

0.34 0.32 0.33

2.05 1.92 1.98

∗

The spectra of this source was obtained by using only the EPIC-pn data.

29